The present invention is directed to ink compositions and, more specifically, the present invention relates to hot melt inks especially useful for acoustic ink printing, processes and apparatuses, reference, for example, U.S. Pat. Nos. 5,121,141, 5,111,220, 5,128,726, 5,371,531, U.S. Ser. No. 176,381, U.S. Pat. No. 5,528,384, the disclosures of which are totally incorporated herein by reference, including especially acoustic ink processes as illustrated in some of the aforementioned copending applications and patents, such as an acoustic ink printer for printing images on a record medium.
More specifically, the present invention is directed to hot melt acoustic ink compositions wherein there can be generated with such inks excellent developed images with acceptable image permanence, excellent projection efficiency on transparencies without a post fusing step, and excellent crease resistance, and wherein the inks possess acceptable, and in embodiments superior lightfastness, and superior waterfastness. Moreover, in embodiments of the present invention there is enabled the elimination, or minimization of undesirable paper curl since water is not present, or very small amounts thereof are selected, in the invention inks, and it is preferred that there be an absence of water, and since water is not present in the inks a dryer can be avoided thereby minimizing the cost of the acoustic ink jet apparatus and process. The inks of the present invention in embodiments thereof are comprised of a colorant and a vehicle, and more specifically, wherein the vehicle is an organo bisamide as illustrated by the following formula ##STR2## wherein R is an alkyl hydrocarbon of from about 2 to about 50 carbon atoms, and R' is an alkylene or polyalkyleneoxide of from about 2 to about 30 carbon atoms. Examples of R include alkyl and aryl, such as methyl, ethyl, propyl, butyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, hexadecyl, octadecyl, stearyl, lauryl, phenyl, benzyl, and anthryl. Examples of R' include alkylenes, such as ethylene, propylene, butylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, tridecylene, hexadecylene, octadecylene, stearylene, laurylene, and the like; poly(ethylene oxide), or poly(propylene oxide) of a molecular weight, M.sub.w, of from about 148 to about 700 grams per mole.
In acoustic ink printing, the printhead produces approximately 2.2 picoliter droplets by an acoustic energy process. The ink under these conditions should display a melt viscosity of about 5 centipoise or less at the jetting temperature. Furthermore, once the ink is jetted onto the paper, the ink image should be of excellent crease property, and should be nonsmearing waterfast, of excellent transparency and excellent fix qualities. In selecting an ink for such applications, it is desirable that the vehicle display low melt viscosity, such as from about 1 centipoise to about 20 centipoise in the acoustic head, while also displaying solid like properties after being jetted onto paper. Since the acoustic head can tolerate a temperature up to about 180.degree. C., and preferably up to a temperature of from about 140.degree. C. to about 160.degree. C., the vehicle for the ink should preferably display liquid like properties such as a viscosity of 1 to about 10 centipoise at a temperature of from about 125.degree. C. to about 165.degree. C., and solidify or harden after jetting onto paper such that the ink displays a hardness value of from about 0.1 to about 0.5 millimeter utilizing a penetrometer according to the ASTM penetration method D1321.
Ink jet printing processes that employ inks that are solid at room temperature and liquid at elevated temperatures are known. For example, U.S. Pat. No. 4,490,731, the disclosure of which is totally incorporated herein by reference, discloses an apparatus for dispensing certain solid inks for printing on a substrate such as paper. The ink dye vehicle is chosen to have a melting point above room temperature so that the ink which is melted in the apparatus will not be subject to evaporation or spillage during periods of nonprinting. The vehicle selected possesses a low critical temperature to permit the use of the solid ink in a thermal ink jet printer. In thermal ink jet printing processes employing hot melt inks, the solid ink is melted by a heater in the printing apparatus and utilized as a liquid in a manner similar to that of conventional thermal ink jet printing. Upon contact with the printing substrate, the molten ink solidifies rapidly, enabling the dye to remain on the surface instead of being carried into the paper by capillary action, thereby attempting to enable higher print density than is generally obtained with liquid inks. Hot melt ink jets are somewhat similar to thermal ink jets, however, a hot melt ink contains no solvent. Thus, rather than being liquid at room temperature, a hot melt ink is typically a solid or semi-solid having a wax-like consistency. These inks usually need to be heated, for example, to approximately 100.degree. C. before the ink melts and turns into a liquid. With hot melt inks, a plurality of ink jet nozzles are provided in a printhead. A piezoelectric vibrating element is located in each ink channel upstream from a nozzle so that the piezoelectric oscillations propel ink through the nozzle. After the hot melt ink is applied to the substrate, the ink is resolidified by freezing on the substrate.
Each of these types of known ink jets, however, has a number of advantages and disadvantages. One advantage of thermal ink jets is their compact design for the integrated electronics section of the printhead. Thermal ink jets are disadvantageous in that the thermal ink has a tendency to soak into a plain paper medium. This blurs the print or thins out the print locally thereby adversely affecting print quality. Problems have been encountered with thermal ink jets in attempting to rid the ink of moisture fast enough so that the ink does not soak into a plain paper medium. This is particularly true when printing with color. Therefore, usually when printing with thermal ink, one needed to use coated papers, which are more expensive than plain paper.
One advantage of a hot melt ink jet is its ability to print on plain paper since the hot melt ink quickly solidifies as it cools and, since it is waxy in nature, does not normally soak into a paper medium. However, hot melt ink jets can be cumbersome in structure and in design, that is, the associated integrated electronics of a thermal ink jet head are considerably more compact than those of a hot melt ink jet head.
In addition, U.S. Pat. No. 4,751,528, the disclosure of which is totally incorporated herein by reference, discloses a hot melt ink jet system which includes a temperature-controlled platen provided with a heater and a thermoelectric cooler electrically connected to a heat pump and a temperature control unit for controlling the operation of the heater and the heat pump to maintain the platen temperature at a desired level. The apparatus also includes a second thermoelectric cooler to solidify hot melt ink in a selected zone more rapidly to avoid offset by a pinch roll coming in contact with the surface of the substrate to which hot melt ink has been applied. An airtight enclosure surrounding the platen is connected to a vacuum pump and has slits adjacent to the platen to hold the substrate in thermal contact with the platen.
Further, U.S. Pat. No. 4,791,439, the disclosure of which is totally incorporated by reference, discloses an apparatus for use with hot melt inks having an integrally connected ink jet head and reservoir system, the reservoir system including a highly efficient heat conducting plate inserted within an essentially nonheat conducting reservoir housing. The reservoir system has a sloping flow path between an inlet position and a sump from which ink is drawn to the head, and includes a plurality of vanes situated upon the plate for rapid heat transfer.
Ink compositions for ink jet printing are known. For example, U.S. Pat. No. 4,840,674, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises a major amount of water, an organic solvent selected from the group consisting of tetramethylene sulfone, 1,1,3,3-tetramethyl urea, 3-methyl sulfolane, and 1,3-dimethyl-2-imidazolidone, which solvent has permanently dissolved therein spirit soluble dyes.
U.S. Pat. Nos. 5,006,170 and 5,122,187, the disclosures of each of which are totally incorporated herein by reference, disclose hot melt ink compositions suitable for ink jet printing which comprise a colorant, a binder, and a propellant selected from the group consisting of hydrazine, cyclic amines, ureas, carboxylic acids, sulfonic acids, aldehydes, ketones, hydrocarbons, esters, phenols, amides, imides, halocarbons, urethanes, ethers, sulfones, sulfamides, sulfonamides, phosphites, phosphonates, phosphates, alkyl sulfides, alkyl acetates, and sulfur dioxide. Also disclosed are hot melt ink compositions suitable for ink jet printing which comprise a colorant, a propellant, and a binder selected from the group consisting of rosin esters; polyamides, dimer acid amides, fatty acid amides, epoxy resins, fluid paraffin waxes, fluid microcrystalline waxes, Fischer-Tropsch waxes, polyvinyl alcohol resins, polyols, cellulose esters, cellulose ethers, polyvinyl pyridine resins, fatty acids, fatty acid esters, polysulfonamides, benzoate esters, long chain alcohols, phthalate plasticizers, citrate plasticizers, maleate plasticizers, sulfones, polyvinyl pyrrolidinone copolymers, polyvinyl pyrrolidone/polyvinyl acetate copolymers, novalac resins; natural product waxes, mixtures of linear primary alcohols and linear long chain amides, and mixtures of linear primary alcohols and fatty acid amides. In one embodiment, the binder comprises a liquid crystalline material. The inks of the present invention are dissimilar than the aforementioned '179 and '187, in that, for example, the invention vehicle selected displays a viscosity of from about 1 to about 20, and preferably 10 centipoise when heated to a temperature of from about 125.degree. C. to about 165.degree. C., such that acoustic energy in the printhead can eject an ink droplet onto paper. Additionally, the vehicles of the present invention display softening points of from about 50.degree. C. to about 100.degree. C. Furthermore, the bisamide vehicles of the present invention also differ substantially and are not disclosed or suggested, it is believed, from the aforementioned '170 or '187 patents.
U.S. Pat. No. 5,021,802, the disclosure of which is totally incorporated herein by reference, discloses a bubble jet ink which comprises 90 to 99.9 percent by weight of aqueous sol gel medium and 0.1 to 1 percent by weight colorant. The inks are thermally reversible sol gels which are gels at ambient temperatures and form liquid sols at temperatures between about 40.degree. and 100.degree. C.
U.S. Pat. No. 5,041,161, the disclosure of which is totally incorporated herein by reference, discloses an ink jet ink which is semi-solid at room temperature. The ink combines the advantageous properties of thermal phase inks and liquid inks. The inks comprise vehicles, such as glyceryl esters, polyoxyethylene esters, waxes, fatty acids, and mixtures thereof, which are semi-solid at temperatures between 20.degree. C. and 45.degree. C. The ink is impulse jetted at an elevated temperature in the range of about 45.degree. C. to about 110.degree. C., at which temperature the ink has a viscosity of about 10 to 15 centipoise. The inks also contain 0.1 to 30 weight percent of a colorant system.
U.S. Pat. Nos. 4,853,036 and 5,124,718 disclose an ink for ink jet recording which comprises a liquid composition essentially comprising a coloring matter, a volatile solvent having a vapor pressure of 1 millimeter Hg or more at 25.degree. C., and a material being solid at room temperature and having a molecular weight of 300 or more, and prepared so as to satisfy the formula B.sub.1 /A.sub.1 .gtoreq.3, assuming viscosity as A.sub.1 cP at 25.degree. C., measured when the content of the solid material in the composition is 10 percent by weight, and assuming viscosity as B.sub.1 cP at 25.degree. C., measured when the content of the solid material in the composition is 30 percent by weight. An ink jet recording process using the ink is also disclosed.
U.S. Pat. No. 5,065,167, the disclosure of which is totally incorporated herein by reference, discloses an ink jet ink including a waxy carrier that is solid at 25.degree. C. and liquid at the operating temperature of an ink jet nozzle and a driver having a critical pressure greater than 10 atmospheres, the carrier and driver being miscible in liquid phase.
U.S. Pat. No. 5,047,084, the disclosure of which is totally incorporated herein by reference, discloses an ink jet ink in the form of a microemulsion of an organic vehicle phase comprising fatty acid and colorant dispersed therein and an aqueous phase containing a surfactant, the vehicle phase preferably being liquid at 70.degree. C. and solid at 20.degree. C.
U.S. Pat. No. 5,226,957, the disclosure of which is totally incorporated herein by reference, discloses water insoluble dyes formulated in a microemulsion-based ink which is waterfast, nonthreading, and bleed-alleviated. The inks comprise (a) about 0.05 to 0.75 weight percent of a high molecular weight colloid, (b) about 0.1 to 40 weight percent of at least two surfactants, comprising at least one surfactant and at least one cosurfactant, (c) about 0.5 to 20 weight percent of at least one cosolvent, (d) about 0.1 to 5 weight percent of at least one water insoluble dye, (e) about 0.1 to 20 weight percent of an oil, and (f) the balance water. The ink forms a stable microemulsion.
While the known compositions and processes are suitable for their intended purposes, a need remains for acoustic hot melt ink compositions suitable for thermal ink jet printing. In addition, there is a need for hot melt ink compositions which are compatible with a wide variety of plain papers. Further, there is a need for hot melt ink compositions which generate high quality, waterfast images on plain papers. There is also a need for hot melt ink jet ink compositions which generate high quality, fast-drying images on a wide variety of plain papers at low cost with high quality text and high quality graphics. Further, there is a need for hot melt ink jet ink compositions which exhibit minimal feathering. Additionally, there is a need for hot melt ink jet ink compositions which exhibit minimal intercolor bleed. There is also a need for hot melt ink jet ink compositions which exhibit excellent image permanence. Further, there is a need for hot melt ink jet ink compositions which are suitable for use in acoustic ink jet printing processes. Additionally, there is a need for hot ink compositions suitable for ink jet printing processes wherein the substrate is heated prior to printing and is cooled to ambient temperature subsequent to printing (also known as heat and delay printing processes). There is also a need for ink compositions suitable for ink jet printing wherein high optical densities can be achieved with relatively low dye concentrations. A need also remains for ink compositions suitable for ink jet printing wherein curling of the substrate, such as paper, subsequent to printing is minimized, or avoided.
Reference is made to copending applications U.S. Ser. No. 624,154, filed concurrently herewith; U.S. Ser. No. 624,156, filed concurrently herewith; and U.S. Ser. No. 624,273, filed concurrently herewith; the disclosures of each application being incorporated herein by reference, illustrate acoustic ink compositions and processes thereof.